The statements in this section merely provide background information related to the present invention and may or may not constitute prior art.
In automatic shifting power transmissions, gear ratio changes are effected by selectively interconnecting members of gear sets. This is accomplished by selectively engaging torque-transmitting devices such as brakes or clutches which rotationally couple together the members of the gear sets either directly or via rotating shafts or members. For each gear ratio change, there is a corresponding sequence of off-going torque-transmitting device disengagement and on-coming torque-transmitting device engagement.
A typical torque-transmitting device is a combination of a piston and a set of friction plates. One subset of the friction plates is rotatably supported by one rotating member and a second subset of the friction plates is rotatably supported by a second rotating member. To join the rotating members for common rotation, a controlled force is applied by the piston to the friction plates to create enough friction for both subsets of the friction plates to rotate in common which in turn joins the two members for common rotation.
Many torque-transmitting devices require hydraulic fluid pressure to move a piston into a position to contact the friction plates and to apply a force to the friction plates. The amount of force required to move the piston into position is less than the force required to compress the friction plates together. Therefore, there is a desire to provide and control variable pressure to the piston to improve the smooth yet quick engagement of the clutches using an efficient hydraulic fluid system.
Additionally, a majority of automatic shifting power transmissions use a transmission control module or controller that receives data and instruction from other sensors or controllers in the vehicle. The transmission controller utilizes the sensor data along with stored program logic to provide instructions to the hydraulic fluid system of the transmission for optimum operation. Vehicle sensors may include speed sensors, throttle position sensors, load sensors, etc. while program controller logic may include shift-timing schedules, etc. Therefore, there is a desire to utilize sensor data in a control method to provide commands to a transmission hydraulic fluid system for improved and optimal operation of clutches and brakes. Accordingly, there is room in the art for an apparatus and method for controlling the application of fluid pressure to torque-transmitting mechanisms to improve gear shift smoothness, timing and efficiency.